This invention relates to a UV curable CF ink, and more particularly, to a UV curable CF ink which may be applied to a substrate inline on a printing press without discoloration or smudging of the ink.
CF (coated front) inks are well known in the art for use in the production of carbonless copy papers. Such inks are typically oil-based and comprise an acidic color developer material which is normally coated on the front side of a carbonless paper set. A CB (coated back) coating containing an initially colorless dye precursor is typically coated on the back side of the carbonless paper such that when adjacent papers are mated together and pressure is applied, the CF and CB coatings react to develop a colored image on the paper. For example, Seitz et al., U.S. Pat. No. 5,169,826, teach a carbonless copy sheet utilizing a CF printing ink including a non-volatile hydrocarbon oil and an acidic color developer such as a phenolic resin. Pinell et al., U.S. Pat. No. 5,084,492, teach a CF printing ink comprising a non-volatile diluent and an acidic color developer such as a phenolic resin. However, carbonless papers currently in use cannot be easily produced inline on a printing press because of discoloration or smudging of the CF coating caused by contact with the CB coating.
It is known that UV curable inks, due to crosslinking of the ink components, are not subject to the problems of smearing or smudging. However, it has heretofore been impractical to use UV curable inks in CF applications because the phenolic resins typically used in CF inks are subject to discoloration when exposed to UV light sources.
Accordingly, there remains a need for a CF ink which may be easily applied to a substrate inline on a printing press and which avoids the problems of discoloration or smudging during processing.
The present invention meets that need by providing a UV curable CF ink including a UV curable ink base and an acidic color developer which does not discolor when subjected to UV light. The ink may be easily applied to a substrate inline on a printing press using conventional letterpress or offset techniques.
In accordance with one aspect of the present invention, a UV curable CF ink is provided comprising a UV curable ink base, an acidic color developer, and a solvent for the acidic color developer. The acidic color developer preferably comprises bis-(3-allyl-4-hydroxy phenyl)sulfone (TGSA) or 4,4-disulfonyl phenol (SFDP). The solvent for the acidic color developer is preferably selected from the group consisting of methyl pyrrolidone, vinyl ethers, and polar acrylate monomers.
The UV curable CF ink also preferably includes a photoinitiator. The ink is preferably curable by UV radiation at a wavelength of from about 200-410 nanometers.
In a preferred embodiment of the invention, the UV curable CF ink comprises about 15 to 30% by weight of a UV curable ink base, from about 20 to 60% by weight of an acidic color developer, and about 10 to 30% by weight of a solvent. The ink also preferably, but optionally, includes from about 1 to 2% by weight of the photoinitiator.
The present invention also provides a method for applying the UV curable CF ink to a substrate having first and second surfaces in which the ink is applied to at least a portion of the first or second surface. The ink is then cured. The resulting CF coated sheet is solvent and heat resistant and may then have indicia printed thereon in laser printers without discoloration or premature coloration of the ink.
Accordingly, it is a feature of the present invention to provide a UV curable CF ink composition which may be easily applied to a substrate inline without the problems of discoloration or smudging. These and other features and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiments, and the appended claims.
The UV curable CF ink composition and method of the present invention provides several advantages over prior oil-based CF inks. First, the ink of the present invention utilizes color developers which do not discolor upon exposure to UV light. Further, because the ink is UV curable, discoloration or smudging of the CF ink by the CB coating is reduced or eliminated. Finally, the UV curable CF ink can be easily produced inline on a printing press using conventional printing techniqiues.
The UV curable ink base included in the CF ink is a clear thick varnish also commonly referred to as xe2x80x9cmixing whitexe2x80x9d or xe2x80x9ctransparent whitexe2x80x9d. A preferred ink base is KC 98-1410 UV, which is commercially available from Kohl and Madden Ink, a division of Sun Chemical Corp. Other suitable base inks include xe2x80x9ctransparent whitexe2x80x9d or xe2x80x9ctransparent inkxe2x80x9d, available from Flint Ink and other commercial suppliers of UV curable inks. The UV curable ink base preferably comprises about 15 to 30% by weight of the ink and preferably has a solids content of from about 25 to 27% by weight. The ink base is preferably substantially free of oils.
Suitable acidic color developers for use in the ink composition include bis-(3-allyl-4-hydroxy phenyl)sulfone, commercially available from Nagase America under the designation TGSA and 4,4-disulfonyl phenol; commercially available from ALFA Chemical, Kingspoint, N.Y. under the designation SFDP. Other suitable color developers include zinc salicylate and phenolic resins, commercially available from Schenectady Chemicals, Inc., Schenectady, N.Y. The color developers should be compatible with the UV curable ink base and should not discolor upon exposure to UV light. The acidic color developer is preferably present in the CF ink composition in an amount of from about 20 to 60% by weight.
A preferred solvent for use in the present invention is methyl pyrrolidone. The solvent functions to dissolve the color developer and keep it in solution so that it remains dispersed in the UV coating after curing while remaining reactive to the color former in the CB coating. Other suitable solvents include vinyl ethers and polar acrylate monomers. The solvent preferably comprises about 10 to 30% by weight of the CF ink composition.
The CF ink composition also preferably includes a photoinitiator to initiate UV curing of the base ink. The photoinitiator is preferably activated when exposed to UV radiation in the range of from about 200 to 410 nanometers. A preferred photoinitiator is commercially available from CIBA Specialty Chemicals Corp., Tarrytown, N.Y. under the designation Darocur 4265 (trademark). Other suitable photoinitiators include benzophenol type photoinitiators such as benzophenone and Irgacure 651 (trademark), acetophenone type photoinitiators, and any free radical light initiated photocatalysts. The photoinitiator is preferably included in an amount of about 1 to 2% by weight.
In the preferred method of making the UV curable CF ink composition of the present invention, the acidic color developer is mixed with the UV curable ink base and heated to about 300xc2x0 F. while adding the solvent until the acidic color developer dissolves into the mixture. The mixture is then cooled to about 150xc2x0 F. before adding the photoinitiator. The ink composition is then preferably cooled until it reaches room temperature, at which point the ink composition is ready to be used.
The UV curable CF ink may be readily applied to a support substrate such as a paper sheet or web using conventional letterpress or offset equipment. A preferred method for applying the ink is letterpress. The ink is preferably applied to a substrate traveling at 250 feet per minute using a 400 watt UV lamp source. A suitable UV lamp source for use in the present invention is commercially available from Fusion Systems, Frederick Md. It should be appreciated that the press speed may be increased with a higher wattage UV curing unit or the use of additional lamp stations.
The UV curable CF ink of the present invention may be used to produce a carbonless copy paper CF sheet or web having a coating on the entire surface or a spot coating of the CF ink applied in any desired pattern. It may also be used to produce a CFB sheet where the CF material is coated on the first side of the support sheet and a CB material is coated on the second side of the support sheet. The resulting CF coated sheet is solvent and heat resistant and may be printed using non-contact printers such as laser printers.